Ethylene glycol dimethyl ether, namely 1,2-dimethoxyethane (DME), is a color less and transparent liquid with an ether smell at normal temperature. It is an aprotic polar solvent with excellent properties, which has a relatively steady nature, and is difficult to participate in a reaction, and is miscible with water and most low carbon (C1-C6) alcohols, ketones and esters at any ratios. It also has a relative strong dissolving capacity to alkali metal compounds. Therefore, it can be the ideal solvent for many organic synthetic reactions. At the same time, it is also widely used as cleaning agent compound, used as additive in textile printing and dyeing, ink painting and fuel. It is also used for synthesizing organic compounds, medical intermediates and the like.
Methods for preparing ethylene glycol dimethyl ether recorded mainly includes: (1) A process of 1,2-dichloroethane reacting with methanol is disclosed in U.S. Pat. No. 3,699,174, in which the metals or metallic oxides of Groups I to V and some transition metals of Groups VI to VIII are respectively used as the catalyst, and the major products are ethylene glycol dimethyl ether and methyl ethyl ether; wherein the percent conversion of the raw material 1,2-dichloroethane is 50% and the selectivity for ethylene glycol dimethyl ether is 24.6%, and the selectivity for dichloromethyl ethyl ether is 46.9%. This process generates many by-products and the yield of the products is not so high; wherein the selectivity for 1,4-dioxane is more than 20%. (2) A process of oxidative coupling reaction of dimethyl ether is disclosed in Japanese patent 60-12089, in which the dimethyl ether is directly oxidized on the surface of the catalyst to obtain ethylene glycol dimethyl ether. However, because that oxygen was added into the reaction system, and dimethyl ether and the product of ethylene glycol dimethyl ether are both flammable substances, there are underlying dangers in this process route. (3) A reaction between dimethyl ether and ethylene oxide is disclosed in U.S. Pat. No. 4,146,736, in which a solid acid catalyst is employed and the percent conversion of the raw material ethylene oxide is nearly 100%, and the selectivity for the product ethylene glycol dimethyl ether is around 65% to 70%, and the selectivity for diethylene glycol dimethyl ether is 15% to 20%, and the sum of the selectivity for tri-, tetra-, pent-ethylene glycol dimethyl ether is around 10%, and the selectivity for 1,4-dioxane is 5% to 7%. However, there are relatively more byproducts in this reaction, and relatively more 1,4-dioxane is generated. (4) Japanese patent 55-104221 has disclosed a method for preparing ethylene glycol dimethyl ether from the dehydration reaction between methanol and ethylene glycol or ethylene glycol monomethyl ether at a reaction temperature of 200□ to 300□; wherein the selectivity for ethylene glycol dimethyl ether in the products is 25%, and the selectivity for diethylene glycol dimethyl ether is 8%, the selectivity for diethylene glycol monomethyl ether is 15%, and there is 1,4-dioxane generated in the process too. (5) U.S. Pat. No. 4,321,413 has disclosed a method for preparing ethylene glycol dimethyl ether at a reaction temperature of 180□ using ethylene glycol monomethyl ether and dimethyl ether as raw materials; wherein the percent conversion of raw material ethylene glycol monomethyl ether is 55.4%, and the selectivity for ethylene glycol dimethyl ether in the product is 62.4%, and the selectivity for 1,4-dioxane is 20% and the selectivity for diethylene glycol dimethyl ether is 16.5%. (6) CN104250206A has disclosed a method for preparing ethylene glycol ether, wherein ethylene glycol and low carbon fatty alcohol are used to prepare ethylene glycol ether in the presence of an acid catalyst, and the solid acid catalyst employed is molecular sieve or zeolite, and the reaction temperature is 20° C. to 250° C., and the reaction pressure is 0.1 MPa to 10 MPa.
In the methods for preparing ethylene glycol dimethyl ether disclosed above, either multiple reactants are employed as the raw materials bring complicated reaction process and complicated by-products, or the reaction condition is too harsh, such as a high reaction temperature. Moreover, there is by-product of 1,4-dioxane existing in all these methods. In addition, when the by-product is dissolved in waste water, it will be hard to be removed using physical separation methods, and the by-product is hard to be biodegraded in nature. At the same time, the by-product may enter human or animal bodies through inhalation, ingestion or skin absorption. When it is cumulated, it will do harm to human or animal bodies because it cannot be metabolic educed.